In the field of cryosurgery, a practitioner freezes diseased or unwanted tissue to destroy the tissue. Cryosurgery has been used for treatment throughout the human body, including cancer treatment, cardiovascular applications, and neural applications, among others.
In one example from the 1980s, practitioners used cryosurgery to treat liver cancer. During the treatment, a practitioner formed relatively large iceballs that were larger than the cancer by 1 cm or more, which created a surgical margin around the cancer. In order to prevent unwanted damage to surrounding tissue, the practitioner used typical clinical imaging technology to monitor the size and location of the iceballs, such as ultrasound (US), magnetic resonance imaging (MRI) and computed tomography (CT). For the relatively large iceballs used for liver cancer treatment in the 1980s, the typical clinical imaging technology was sufficient to monitor the iceball size and location.
Over time, practitioners have used cryosurgery to treat increasingly more intricate areas of the body, which include relatively fine tissue and structures. Treatment of these intricate areas requires increasingly precise monitoring of the size and location of the iceballs, in order to prevent damage to surrounding tissue and organs. For instance, during treatment of the prostate for prostate cancer, a practitioner carefully avoids damaging the rectum, bladder, and neurovascular bundle, which are all located within a few mm of the prostate. Imprecise monitoring of the iceball size and location during prostate treatment can damage these adjacent organs, and can lead to complications, such as fistulas, incontinence, and impotence. As another example, during treatment of atrial fibrillation, a practitioner uses a cryoballoon in the pulmonary vein to form a 2 mm-thick iceball throughout the vein wall. During the procedure, the practitioner carefully avoids freezing adjacent tissue, such as the lung, esophagus, and phrenic nerve.
In general, the typical clinical imaging technologies of ultrasound, magnetic resonance, and computed tomography do not have a resolution fine enough to accurately monitor iceball formation in the more intricate areas of the body. Accordingly, there exists a need for a monitoring system and method that can monitor an edge of a frozen region with sufficient precision to be used for the relatively thin tissues in the more intricate parts of the human body. Such a monitoring system and method could have other applications, such as monitoring heat-based elements.